1. Field of the Invention
The invention relates to a liquid crystal display module, more particularly, to a liquid crystal display module having improved display quality and productivity.
2. Description of the Related Art
Liquid crystal display (hereinafter, LCD) devices trend towards gradually wider applications due to their lightness, thinness, and low power consumption. In accordance with this trend, LCD devices find use in office automation devices, audio/video devices and the like.
An LCD device adjusts the transmittance of light in accordance with an image signal applied to multiple control switches arranged in a matrix-type array in order to display desired pictures in a screen.
Generally, an LCD device includes a liquid crystal display module and a driving circuitry for driving the liquid crystal display module.
The liquid crystal display module includes a liquid crystal display panel having liquid crystal cells arranged in a matrix between two glass substrates, and a backlight unit irradiates light onto the liquid crystal display panel. The liquid crystal display panel and the backlight unit must engage with each other in an integral shape so as to prevent a light loss, and also be protected from damage caused by external impacts. To this end, a casing encloses the back light unit as well as the edges of the liquid crystal display panel.
There are two types of back light units for a liquid crystal display module: i) a direct-below-type, and ii) an edge-type.
The edge-type back light unit has a fluorescent lamp installed on the outside of a light guide plate, and thus the light from the fluorescent lamp is incident to the entire surface of the liquid crystal display panel by using a transparent light guide plate. The direct-below-type back light unit has a light source arranged at a rear surface of the liquid crystal display panel, and the light source directly radiates light to the entire surface of the liquid crystal display panel. Compared with the edge-type back light unit, the direct-below-type back light unit has advantages in that multiple light sources can be used to improve brightness and that the light-emitting surface can be widened.
FIG. 1 shows a perspective view illustrating a related art liquid crystal display module employing a direct-below-type back light unit. FIG. 2 shows a sectional view representing the liquid crystal display module taken along line I-I′ in FIG. 1.
In FIG. 1 and FIG. 2, the liquid crystal display module 1 employing the direct-below-type back light unit includes a main support 14, a back light unit and a liquid crystal display panel 6 stacked in an interior of the main support 14. A top case 2 encloses the edge of the liquid crystal display panel 6 and the side of the main support 14.
The liquid crystal display panel 6 includes a color filter array substrate 5 and a thin film transistor (TFT) array substrate 3. Liquid crystal materials are injected between the color filter array substrate 5 and the TFT array substrate 3. The liquid crystal display panel 6 is provided with a spacer (not shown) that constantly keeps a gap between the color filter array substrate 5 and the TFT array substrate 3. The color filter array substrate 5 is provided with a color filter, a common electrode and a black matrix (not shown). Signal lines such as a data line and a gate line (not shown) are formed on the TFT array substrate 3 of the liquid crystal display panel 6. A thin film transistor (TFT) is formed at an intersection between the data line and the gate line. The TFT switches a data signal to be transmitted from the data line to the liquid crystal cell in response to a scanning signal (i.e., a gate pulse) from the gate line. A pixel electrode is formed at a pixel area between the data line and the gate line. A pad area is formed at one side of the TFT array substrate 3 and is connected to each of the data line and the gate line. A tape carrier package (not shown), having a driver integrated circuit mounted thereon for applying a driving signal to the TFT, is attached onto the pad area. This tape carrier package applies a data signal from the driver integrated circuit to the data line. Further, the tape carrier package supplies a scanning signal to the gate line.
An upper polarizing sheet attaches onto the color filter array substrate 5 of the liquid crystal display panel 6, and a lower polarizing sheet attaches onto the rear side of the TFT array substrate 3 of the liquid crystal display panel 6.
The main support 14 is made from a molded material, and its inner lateral wall surface is molded into a stepped coverage face. The stepped coverage face has a securing part formed therein in which the back light unit and the liquid display panel 6 are accommodated. The back light unit that irradiates light onto the liquid crystal display panel 6, and the liquid crystal display panel 6 that adjusts the transmittance of light irradiated from the back light unit to display a picture, are stacked inside the main support 14.
The back light unit includes multiple lamps 20 irradiating light onto the liquid crystal display panel 6, multiple lamp holders 22 on which the lamps 20 are fixedly mounted, a diffusion plate 10 that diffuses incident light received from the lamps 20 to irradiate the light onto the liquid crystal display panel 6, a lamp housing 18 arranged on the rear surface of the lamps 20, and multiple optical sheets 8 stacked on the diffusion plate 10.
A cold cathode fluorescent lamp is mainly used for the lamps 20. Each of the lamps 20 includes a glass tube, inert gases within the glass tube, and a cathode and an anode installed at the respective opposite ends of the glass tube. The inert gases are injected in the glass tube. A passivation film is formed on the inside wall of the glass tube, and phosphorus is applied to the inside wall of the glass tube. The light generated from the lamps 20 is incident to the diffusion plate 10.
The diffusion plate 10 directs the light received from the lamps 20 toward the front surface of the liquid crystal display panel 6, and the diffusion plate 10 diffuses the light to have a uniform distribution over a broad area, so that the diffused light is irradiated to the liquid crystal display panel 6. The diffusion plate 10 includes a transparent resin film having both surfaces coated with light-diffusion materials.
The lamp housing 18 includes a reflection sheet 12 and a bottom cover 16 arranged on the rear surface of the reflection sheet 12.
The bottom cover 16 has a bottom surface and an inclined surface extending from the bottom surface. That is, the bottom surface and the inclined surface of the bottom cover 16 are bent like a step. The reflection sheet 12 is stacked on the bottom cover 16.
The reflection sheet 12 is arranged on the rear surface of the lamp 20. The reflection sheet 12 is made of a light-reflecting material that takes the same shape as the bottom cover 16. Moreover, the reflection sheet 12 has a bottom surface that overlaps the bottom surface of the bottom cover 16 and also has an inclined surface correspondingly bent to the inclined surface of the bottom cover 16. The reflection sheet 12 adheres to the bottom surface and the inclined surface of the bottom cover 16 using a double-sided adhesive tape (not shown). The reflection sheet 12 reflects the light directed toward the rear surface and the side surface of the lamps 20 toward the liquid crystal display panel 6 to thereby improve the efficiency of the light irradiated on the liquid crystal display panel 6.
The light exiting from the diffusion plate 10 serves as diffused light that widens the viewing angle. The efficiency of the light incident to the liquid crystal display panel 6 becomes high when the incident light is perpendicular to the liquid crystal display panel 6. To this end, the optical sheets 8 are disposed on the diffusion plate 10. The optical sheets 8 make the light exiting from the diffusion plate 10 to project perpendicularly, thereby improving the efficiency of the light. According to the scheme, the light exiting from the diffusion plate 10 reaches the liquid crystal display panel 6 via the optical sheets 8.
The top case 2 has a square band shape having a plane part and a side part bent perpendicularly. The top case 2 encloses the edge of the liquid crystal display panel 6 and the main support 14.
FIG. 3 shows a perspective view illustrating a related art back light unit of the liquid crystal display module shown in FIG. 1.
High voltage generates heat in the glass tube of the lamp 20 used for a light source of the related art back light unit shown in FIG. 3. If the heat occurs in the glass tube, then an exhaustion amount of mercury gas filled inside the glass tube largely increases. As a result, the brightness of light emitted from the lamp 20 becomes uneven, thereby lowering the reliability and reducing the life span of the lamp 20. Further, if any one of multiple lamps 20 becomes damaged or is inferior, then the brightness of the back light unit suddenly decreases, and implementing a scanning back light driving method capable of improving the display quality of the liquid crystal display module 1 by controlling the brightness of each part of the back light unit becomes impossible. Also, the complex arrangement of the back light unit requires a lot of time to assemble the liquid crystal display module 1, which entails lower productivity.